I need a scanner that is not prone to overloading and that does not have sensitivity issues.
If you're looking for a scanner that isn't prone to overloading, then stay away from GRE or GRE-built Radio Shack models, and stick with Uniden.
Your Pro-433 was built by Uniden and should not suffer from front end overload. If it does, you may have a very strong local signal that would overload just about any receiver, which you should investigate and deal with before buying a new scanner as the solution.
Are you experiencing overload on particular bands or a range of frequencies? Is the Pro-433 setup as a base scanner, or are you mobile? External antenna or the back-of-set antenna? Are there any nearby AM/FM transmission towers, paging towers, cell phone towers, etc.?